This invention is an improvement in my earlier original invention for which a patent application was filed Mar. 20, 1981, Ser. No. 245,945. The original invention makes use of the technologies of radar, exploration seismology and air transportation to provide a highly-mobile and economical system of geophysical exploration for petroleum and other minerals. Use is made of the Seismo-electric (SE) and Electro-seismic (ES) effects to momentarily alter the absorption in, and reflection or scattering from, the earth's surface of electromagnetic (radar) waves transmitted from, and received by, an aircraft, to thereby modulate seismic information on the reflected, scattered and received waves. The present invention applies the same basic apparatus as the original invention and, additionally, provides a great improvement in how the useful seismically-modulated radar wave signals are separated from the bulk reflected and scattered electromagnetic wave signals which might otherwise mask the smaller seismically modulated responses.
In the original invention, several methods and means of cancelling, or nulling, the bulk reflections were provided. In all of these a phase and amplitude balance was obtained as the radar scanned the terrain being explored, prior to the initiation of seismic responses; i.e., prior to dropping a weight or detonating an explosive charge, and the bulk reflections and scatterings thereby nulled in the receiving apparatus.
It is clear that the goodness of these methods and means depends upon the goodness of the phase and amplitude balance that can be obtained (the null). Since the balance is over at least one complete scan of the radar antenna (Practically, it is over many complete scans.), it is a broad average null covering a relatively large surface and, as such, cannot possibly be as good as might be desired. The most desirable arrangement would be one wherein the balance (the null) was automatically obtained for each and every small segment of the scan of the radar antenna. This kind of balance, or null, would then leave only the seismic response of each small segment of earth surface to be received, amplified, processed, and passed to form PPI pictures and recorded for additional processing at a later time. The object of this invention is to provide method and means whereby this ideal result is obtained.